When a subsea well has been drilled, the wellhead is typically terminated in a base or guide template which rests on the ocean floor. It is necessary from time to time to lower equipment from the surface of the ocean to the ocean floor and to attach or mate that equipment to other equipment or fixtures on the base. This requires a means for guiding the equipment being lowered to the vicinity of the base and for accurately aligning that equipment with its mating fixture on the base once it has arrived.
These guidance and alignment functions are served by guidelines which descend from the ocean surface to the tops of guideposts which rise from the base, preferably by being inserted in a guidepost-receptacle on the base designed for the purpose. Typically, the guidepost-receptacle will have an annular depression or groove on its inner surface and the guidepost will have retractable dogs or other locking features protruding from its outer surface. As the guidepost is inserted into the guidepost-receptacle, the retractable dogs snap outward into the groove when the guidepost reaches full insertion. The dogs then act as locking devices to retain the guidepost in the guidepost-receptacle until removal of the guidepost is required.
There are various methods for removal of a guidepost from a guidepost-receptacle for retrieval. The dogs can be retracted by downward force on a component of the guidepost, by frangible devices or by manipulation of the guidepost by a remotely operated vehicle on the ocean floor. Use of force on the top of the guidepost or a component thereof is undesirable because of the tendency to buckle the component, especially if it is very long. This effectively limits the guidepost length in order to prevent buckling. Use of frangible release mechanisms can be unreliable. Manipulation of the base of the guidepost or the guidepost-receptacle by a remotely operated vehicle can be impossible because the areas around the base are not always accessible.